1. Field of the Invention
The invention relates generally to image processing methods and apparatus and more particularly, to the method and apparatus used for processing coarse scan/fine print data.
2. Description of the Prior Art
The scanning binary encoding, compression, transmission and reproduction of data is well known in the prior art. Prior art image processing devices which perform the enumerated functions are affected by at least two almost irreconcilable factors, namely: resolution and device cost. Any attempt to improve one factor appears to adversely affect the other factor and vice versa. The resolution of an image processing device refers to the fidelity with which a copy of an original document (such as textual and/or continuous tone material) is reproduced. In the prior art, the reproduction of high fidelity copies require elaborate high cost electronic gadgets which augment the overall system cost.
Several devices and methods have been used in the prior art to reconcile the disparity between high fidelity reproduction and cost. One of such prior art methods is the so-called coarse-scan/coarse-print method. Generally, the images and/or data are coarsely scanned and coarsely printed. In other words there is a 1:1 resolution between an original document and a reproduced copy. It is worthwhile noting at this point, that the amount of data generated from a document to be reproduced is directly dependent on the relative coarseness with which the document is scanned. As such, the coarser a document is scanned, the lesser amount of data will have to be processed (i.e. digitized, encoded etc.) for transmission to a reproducing device. Since the volume of data is relatively small, the cost of the system is relatively low.
Conversely, coarse-scan/coarse-print documents are often of poor quality, primarily because the amount of data generated from the coarsely scanned document is insufficient to reproduce the same.
Coarseness generally refers to the number of picture elements (PELs) per unit area. Therefore, the coarser the scanning of a document, the lesser amount of data is available regarding the contents of the document. In a system wherein the resolution ratio is 1:1, the reproduced copy is no better than the degree of coarseness with which the original document is being scanned. In fact, the resolution ratio of the reproduced copy is often less than one due to degradation of the data during processing and transmission. The net result is that although the cost of the coarse-scan/coarse-print system is relatively low, the quality of the reproduced copy is poor.
Another prior art method is the so-called fine-scan/fine-print method. In this method a fine-scanned device is used to scan the document and a fine-reproduction device is used to print the reproduced copy. Usually a document is finely scanned if the document is scanned at approximately 720 PELs per inch. Likewise, the document is finely printed if it is reproduced at about 720 PELs per inch. Although this method produces high quality reproductions of original documents, the system cost is relatively high. The high cost stems from the fact that a large amount of data has to be processed and transmitted to the reproducing device.
Still another method used in the prior art to reconcile cost and picture quality in facsimile devices or image processing devices is the so-called coarse-scan/print-fine method. In this method the document is coarsely scanned and finely printed. In other words, the resolution ratio of the reproduced copy is different from the resolution ratio with which the original document is scanned. Usually, the resolution ratio of the copy is greater than the resolution ratio of the original, for example, 1:N (where N is greater than 1).
U.S. Pat. No. 3,573,789 is one example of prior art coarse-scan/print-fine devices. The subject patent teaches an apparatus and method for expanding the resolution of data images. The method expands each data bit which was assigned a physical area in the image to be displayed into a plurality of data bits which are still associated with the same physical area of the image to be displayed. The expansion of data bits is obtained by comparing each data bit with its surrounding eight data bits. If the original data bit signified that the area was to be displayed, then the area will still be displayed. If the original data bit signified that the area was not to be displayed, then one or more of the newly generated plurality of data bits will be displayed as a function of the surrounding eight data bits within the original data image.
U.S. Pat. No. 4,032,977 exemplifies a prior art device wherein grey scale information is used to expand the resolution of a reproduced document. The patent discloses an interpolator which predicts a grey scale value for each picture element (PEL) of video output data on the basis of the quantized levels of an m.times.n metrix video input data elements. The interpolator is constructed in accordance with a predetermined probabilistic information to carry out a maximum likelihood estimation process so that the grey scale information is introduced with minimum statistical errors.
U.S. Pat. No. 4,124,870 is yet another example of prior art devices wherein coarsely scanned data is finely printed by utilizing grey scale information. According to this method, eight sums are obtained of various groups of three, peripheral PELs surrounding the PEL to be reproduced. The peripheral PELs are located symmetrically (i.e. on both sides of bisecting lines, vertical, horizontal and two 45.degree. lines) with respect to the PEL to be reproduced. A particular matrix of print dot placement is selected from a prestored group of print dot patterns. The selected pattern becomes the model from which the data is finely reproduced. The matrix of print dot placement is selected according to the largest pattern sum of the eight possible cases.
Although the above-described coarse-scan/print-fine device shows a definite improvement over either the fine-scan/print-fine or the coarse-scan/coarse-print devices, the cost of the coarse-scan/fine-print device appears to be still relatively high. Among the factors which tend to augment the cost of the device is the use and/or processing and transmission of unnecessary grey scale information to reconstruct the reproduced document. Of course, there will have to be a trade-off between cost and quality, however, one does not have to sacrifice cost for quality or vice versa. In fact, the present invention discloses a scan-coarse/fine-print device for reproducing high quality print at relatively low cost.